DBMS ⇝

database management system

(DBMS) A suite of programs which typically manage
large structured sets of persistent data, offering ad hoc
query facilities to many users. They are widely used in
business applications.

A database management system (DBMS) can be an extremely
complex set of software programs that controls the
organisation, storage and retrieval of data (fields, records
and files) in a database. It also controls the security and
integrity of the database. The DBMS accepts requests for data
from the application program and instructs the operating
system to transfer the appropriate data.

When a DBMS is used, information systems can be changed much
more easily as the organisation's information requirements
change. New categories of data can be added to the database
without disruption to the existing system.

Data security prevents unauthorised users from viewing or
updating the database. Using passwords, users are allowed
access to the entire database or subsets of the database,
called subschemas (pronounced "sub-skeema"). For example, an
employee database can contain all the data about an individual
employee, but one group of users may be authorised to view
only payroll data, while others are allowed access to only
work history and medical data.

The DBMS can maintain the integrity of the database by not
allowing more than one user to update the same record at the
same time. The DBMS can keep duplicate records out of the
database; for example, no two customers with the same customer
numbers (key fields) can be entered into the database.

If the DBMS provides a way to interactively enter and update
the database, as well as interrogate it, this capability
allows for managing personal databases. However, it may not
leave an audit trail of actions or provide the kinds of
controls necessary in a multi-user organisation. These
controls are only available when a set of application programs
are customised for each data entry and updating function.

A business information system is made up of subjects
(customers, employees, vendors, etc.) and activities (orders,
payments, purchases, etc.). Database design is the process of
deciding how to organize this data into record types and how
the record types will relate to each other. The DBMS should
mirror the organisation's data structure and process
transactions efficiently.

Organisations may use one kind of DBMS for daily transaction
processing and then move the detail onto another computer that
uses another DBMS better suited for random inquiries and
analysis. Overall systems design decisions are performed by
data administrators and systems analysts. Detailed database
design is performed by database administrators.

The three most common organisations are the hierarchical
database, network database and relational database. A
database management system may provide one, two or all three
methods. Inverted lists and other methods are also used. The
most suitable structure depends on the application and on the
transaction rate and the number of inquiries that will be
made.

Database machines are specially designed computers that hold
the actual databases and run only the DBMS and related
software. Connected to one or more mainframes via a
high-speed channel, database machines are used in large volume
transaction processing environments. Database machines have a
large number of DBMS functions built into the hardware and
also provide special techniques for accessing the disks
containing the databases, such as using multiple processors
concurrently for high-speed searches.

The world of information is made up of data, text, pictures
and voice. Many DBMSs manage text as well as data, but very
few manage both with equal proficiency. Throughout the 1990s,
as storage capacities continue to increase, DBMSs will begin
to integrate all forms of information. Eventually, it will be
common for a database to handle data, text, graphics, voice
and video with the same ease as today's systems handle data.